Please help in creating a trigger

Hello
We use Oracle 8 database in our college. An Oracle application from outside supplier enables us to enrol students. Enrolments are processed from many PCs on WAN, which includes several sites. Recently the system started to behave a bit naughty: one very important parameter, number of PC, on which the enrolment is processed, SOMETIMES is not recorded in the database. I need to create a trigger, which would have fired, if in the record being inserted into the table there is NULL in the field, where should be computer number. Ideally, I'd like to get this number (to read from a file, for example), to insert it into the record and only then to insert the record into the table. Is this possible? If yes, would you mind to point me in the direction of a trigger code, which I could use as an example.
If Oracle trigger cannot be programmed to read from a file, another appropriate action would be to cancel inserting the record and to show a message on the screen prompting the user to click SAVE button once more. A sample of trigger code would be very appreciated. Thank you.
Galina Received on Thu Sep 05 2002 - 16:34:49 CEST